The present invention relates to thrust reversers for turbofan engines and, in particular, to thrust reversers of the type having a translating sleeve, a type of thrust reverser that is often termed a xe2x80x9ccascade type.xe2x80x9d
For normal rearward air flow through the air duct of a turbofan engine that has a cascade type thrust reverser, the translating sleeve resides in a closed position in which its forward end engages the rearward side of a torque box that forms the forward bulkhead of the thrust reverser assembly. Inner wall members of the translating sleeve form the outer wall of the rear portion of the air duct. Outer wall members of the translating sleeve are faired aerodynamically to the forward cowling of the engine.
For reverse air flow, the translating sleeve is moved rearwardly away from the forward bulkhead, leaving an outlet opening rearwardly of the forward cowling for air to be discharged generally radially from the air duct. The reverser also provides for blocking of the air duct at a location rearwardly of the outlet opening. One form of blocking system is a number of blocker doors that are pivotally mounted on the translating sleeve and are coupled by blocker door links to a cowling around the gas turbine of the engine. When the translating sleeve moves rearwardly upon deployment of the reverser, the linkages pivot the blocker doors down to a position in which they block the air duct. In another form of blocking system, the fixed inner wall members of the translating sleeve block the air duct when the translating sleeve is in the open, reverse-thrust position by having their forward, radially inner ends brought into proximity with a divergent portion of the inner wall of the air duct. When the translating sleeve is deployed for reverse thrust of the air flow, a cascade array, a series of circumferentially extending, curved deflector blades, in the outlet opening formed between the forward bulkhead and the forward end of the translating sleeve redirects the air flow in the air duct so that it flows outwardly and forwardly.
Inadvertent deployment of a turbofan engine thrust reverser during flight is an unthinkable event. Therefore, it is well-known to provide multiple locks to hold the translating sleeve of a cascade thrust reverser in the closed position and to design the locks so that they will not unlock in the event of a thrust reverser control system failure. All translating sleeve lock systems include mechanical locks integrated with the linear actuators that move the translating sleeve between the closed, forward thrust position and the open, reverse-thrust position. The actuator locks usually have mechanical springs that keep them closed and electrical (solenoidal) or hydraulic releasing elements. Despite careful design and installation, the actuator locks are not failsafe. For example, electrical faults in the control wiring, which can be caused by incidents such as a turbine rotor burst, can cause the actuator locks to release and also initiate operation of the actuators to open the translating sleeve.
In addition to the locks on the actuators, it has been proposed that the translating sleeve itself be provided with a latch that is controlled separately from the actuator locks and couples the translating sleeve to a fixed part of the thrust reverser assembly so that the translating sleeve cannot move toward open, even if the actuators are unlocked and are applying force to the translating sleeve. An example of a latch for a translating sleeve of a cascade type thrust reverser is described and shown in U.S. Pat. No. 6,021,636.
Previously proposed latches for translating sleeves of cascade type thrust reversers have involved latching the forward end of the translating sleeve to the torque box. The torque box is a robust element of the thrust reverser assembly and thus well-suited as a strong mounting location for a latch. The torque box is also located conveniently to the region forward of the torque box and within the forward outer engine cowling where space is available for valves, piping and wiring associated with a translating sleeve latch. Thus, the location of a translating sleeve latch on the forward end of the translating sleeve has advantages.
Locating a translating sleeve latch on the torque box places it relatively near the integrated mechanical locks associated with the translating sleeve actuators. Although it is extremely unlikely, there is nonetheless a chance that a turbine rotor failure or some other event could damage the translating sleeve latch in a manner that releases it and at the same time, due to their nearby location, damage components of the translating sleeve actuators in a manner that causes them to be released as well and to operate and deploy the thrust reverser to the reverse thrust position.
An object of the present invention is to provide a latch for the translating sleeve of a cascade type thrust reverser that is located remotely from the translating sleeve actuators, thus reducing the chance that a turbine rotor failure or some other event could damage both the translating sleeve latch and the translating sleeve actuator system in a manner that would cause the translating sleeve to move to the reverse thrust position. It is also an object to provide a latch for a translating sleeve that is of simple construction, light in weight, and requires little space. Yet another object is to provide a translating sleeve latch that is functionally highly reliable.
The foregoing objects are attained, in accordance with the present invention, by a thrust reverser for an air duct of a turbofan engine that includes a torque box structure adapted to be mounted on the rearward end of a forward outer fan housing of an air turbine of the engine, a track beam affixed to and extending rearwardly from the torque box structure and having an elongated slideway, a slider received by the slideway for sliding movement, and a translating sleeve coupled to the slider. A releasable lock mechanism mounted on the track beam includes a lock member having a locking portion that when in a locked position of the lock member is engageable with the slider to lock the translating sleeve in the closed position and when in an unlocked position is disengaged from the slider so that the translating sleeve may be moved to the open position.
The location of the lock mechanism on a track beam of the thrust reverser, a position that makes it somewhat remote from the locks associated with the actuators, reduces the chance that a rotor burst will damage both the actuator locks and the lock associated with the translating sleeve itself. The association of the lock mechanism with a track beam and the engagement of the locking portion of the lock member with a slider provides a strong connection between the locked translating sleeve and the torque box structure and also permits the lock mechanism to be of a relatively simple construction. For example, the lock mechanism makes it unnecessary to incorporate structure in the translating sleeve to accept a latch lever.
In an advantageous arrangement, the lock member is a lock pin that translates along an axis, thus avoiding the need for, for example, a pivoting latch hook and an associated bracket. In most cases, it is preferred that the locking portion of the lock pin be received in the slideway of the track beam adjacent and rearwardly of the rearward end of the slider. That location avoids the need to have a notch or hole in the slider to accept the lock pin. When there is insufficient room at the rearward end of the track beam to allow the lock pin and an actuator associated with the lock pin to be located to be engageable with the rearward end of the slider, the lock pin and actuator can be located remotely from the rearward end of the track beam, and a hole or notch can be provided in the slider to accept the locking portion of the lock pin.
In desirable arrangements, the locking portion of the lock pin is movable with a close sliding fit through a hole in a wall member that defines a portion of the slideway associated with the track beam. In such arrangements, the pin is robustly supported by the wall member and is loaded in shear when in the locked position, thus avoiding the imposition of large flexural stresses on the lock pin.
In preferred embodiments of the present invention, the lock member is moved between the locked and unlocked positions by a linear actuator that has an actuating rod coupled to the lock pin. In an arrangement that uses limited space efficiently, the actuator may be positioned such that the actuating rod is movable along an axis that is substantially parallel to the axis of the thrust reverser, and the lock pin is movable along an axis substantially perpendicular to the axis of the actuating rod. Where space permits, the actuator may be mounted with its actuating rod perpendicular to a plane that includes the axes of the thrust reverser and the slideway with which the lock is associated. Such an arrangement has the advantages of mechanical simplicity and light weight.
When a linear actuator is used to move the lock pin and the actuator is oriented longitudinally of the track beam, various drive couplings may be provided between the output element of the actuator and the lock pin. Generally, a cam coupling will be suitable. The cam coupling may be a simple face cam with a cam surface oblique to the axes of the lock pin and the output element of the actuator. Another suitable cam coupling includes a slot in the lock pin, a cam follower shaft transecting the slot, and a slide block that is received in the slot and has a cam slot receiving the follower shaft.
As is well-known to those skilled in the art, there are various designs of cascade-type thrust reversers. Some have a unitary translating sleeve that is supported by a slideway on each of a pair of track beams that straddle a pylon or strut by which the engine is mounted on the aircraft. Others have two translating sleeve units, one on each side of a diametrical plane of the engine, which are mechanically coupled at a location diametrically opposite the pylon or strutxe2x80x94designs of this type usually are hinged to the track beams adjacent the pylon or strut so that they can be swung open for access to the engine. In the aforementioned designs, it suffices to provide a single lock mechanism on one of the track beams. In thrust reversers having two separate translating sleeve units, which are independently mounted on upper and lower pairs of track beams and not mechanically connected, a lock mechanism is provided on a track beam of each translating sleeve unitxe2x80x94i.e., two lock mechanisms, one for each unit, are provided.
The actuators associated with the lock pins of lock mechanisms embodying the present invention may be hydraulically, pneumatically, or electrically powered and may have either linear or rotary outputs.
For a better understanding of the invention, reference may be made to the following description of exemplary embodiments, taken in conjunction with the accompanying drawings.